The present invention generally relates to a line set-up system and, more particularly, to a line set-up system adapted for time division multiplex access for a subscriber optical telecommunication line network having an n-branch star configuration.
FIG. 2 of the accompanying drawings schematically illustrates part of a conventional n-branch star configuration where a network side line terminating set 4 is connected to n user's side line terminating sets 5-j (j=1, 2, 3, . . . , n) by way of an optical splitter 3. The network side line terminating set 4 comprises a line information transfer circuit 41 and a network side line terminating circuit 42. The line information transfer circuit 41 transfers externally supplied line information Sa such as the phase of transmission and the burst length of transmission burst signals of each user's side line terminating set 5-j to the remaining user's side line terminating sets 5-j by way of the network side line terminating circuit 42.
The network side line terminating circuit 42 terminates n branched optical lines and inserts the line information Sa into the transmission/reception burst signal. On the other hand, each of the user's side line terminating sets 5-j comprises a user's side line terminating circuit 51-j (only 51-1 is shown), a user's side line set-up control circuit 52-j (only 52-1 is shown), a line set-up main memory 53-j (only 53-1 is shown) and a transmission burst control circuit 54-j (only 54-1 is shown).
The user's side line terminating circuits 51-j terminates the related one of the n branched optical lines and executes the extraction of the line information Sa and the line control information from the transmission/reception burst signal and the insertion of the line information detection output signal into the burst signal. The user's side line set-up control circuit 52-j, upon positively acknowledging a normal reception by detecting N successive conformities on the part of the line information from the network side line terminating set 4 or normal detection, transmits a write control signal to the line set-up main memory 53-j, whereas, upon negatively acknowledging a normal reception or abnormal detection, it transmits a stop control signal to the transmission burst control circuit 54-j. The line set-up main memory 53-j stores the line set-up information under the control of the user's side line set-up control circuit 52-j and transfers the stored information to the transmission burst control circuit 54-j. The transmission burst control circuit 54-j controls the phase and the bit length of the transmission burst signal according to the information stored in the line set-up main memory 53-j.
With a subscriber optical telecommunication network having a configuration as described above, if the line set-up information transmitted from the network side line terminating set to a user's side line terminating set is not properly detected due to a bit error occurred on the optical fiber or normal detection is determined, the transmission of burst signals has to be suspended to make the line unusable in order to prevent any interference of burst signals transmitted from other normal user's side line terminating sets by the burst signal transmitted on the basis of the not-properly-detected information.
While this problem may partly be dissolved by adding an error correction code to the line information, then the total number of bits to be transferred for line set-up operation inevitably increases and a complex error correction code decoding circuit adapted to decode such error correction codes has to be incorporated so that consequently the overall circuit configuration will become bulky and too redundant.